plant diseases

Plant diseases causes serious losses to crop production. They may kill plants
completely, but more often they simply reduce the yield. Most plant diseases
are caused by microorganisms which infect the tissues, the most important
being fungi, including mildew, rusts, and
smuts. Control methods are based on fungicides. Viruses are the next most damaging group of plant pathogens. Most of them are carried
by aphids and other sap-sucking insects and control is largely a matter
of controlling these insect-carriers. Bacteria are less important, their main role being in secondary infection, causing
the tissues to rot. Deficiency diseases are caused by a lack of available
minerals in the soil. Insect pests, such as the boll weevil on cotton, can
also cause serious crop damage.